1. Field of the Invention
The present invention relates to an aqueous dispersant solution. More specifically, the invention relates to a stable aqueous dispersant solution containing elevated levels of ethylene oxide/propylene oxide (EO/PO) nonionic block copolymer, and methods of making, and using the same. The dispersant solutions are particularly useful in the production of suspension concentrates, solid/liquid dispersions, or emulsions.
2. Brief Description of the Prior Art
Suspension concentrates of particles in an aqueous medium are generally known in the art. Also generally known are dispersants that are used to stabilize the suspension concentrates. Anionic dispersants, for example, promote stability by increasing the electrostatic repulsion forces of the particles. Nonionic block copolymer dispersants promote stability by steric means by forming around the particles' physical barriers that keep them separated and prevent agglomeration from inter particle collisions. Of interest here are suspension concentrates containing nonionic block copolymer dispersants in the form of waxy pastes that melt at 30.degree. to 50.degree. C., resolidify rapidly on contact with their container and other contents of the container at ambient temperatures, and then dissolve very slowly. Illustratively, the nonionic block copolymer would resolidify on contact with water and surfaces such as pipelines and agitating blades, and then dissolve rather slowly in water.
This apparent incompatibility of the nonionic block copolymers compels formulators to prepare pre-formulated solutions of the nonionic block copolymer dispersants. The nonionic block copolymer dispersant is pre-formulated with a water-miscible solvent before it is added to formulation process streams operating at ambient temperatures. However, the maximum concentration of nonionic block copolymer in this pre-formulated solution has been about ten percent. Above the ten percent concentration, the pre-formulated solution generally encounters problems such as unduly high viscosity at ambient temperature, and/or a rapid cloud point transformation to a solid gel structure when the solution is heated.
There is, therefore, a need for both formulation and production processing approaches that will feasibly provide a pre-formulated aqueous dispersant solution that contains a higher concentration of nonionic block copolymer. The present invention provides a formulation approach that achieves the target EO/PO nonionic block copolymer concentration of twenty percent and higher, and a feasible process for preparing and using the same.